1. Field of the Invention
This invention relates generally to roller hearth furnaces, and more specifically to such furnaces which are used to heat sheets of glass prior to a quench that tempers the glass.
2. Description of the Prior Art
Glass sheets can be tempered by first heating the sheets and then suddenly cooling them to thereby change the mechanical properties of the glass. The tempering operation increases the strength of the glass and also causes the glass to break into small pieces that are dull and relatively harmless instead of into large, sharp pieces.
To perform the tempering of glass sheets, roller hearth furnaces have been developed in the past to heat the glass sheets prior to their cooling which is usually performed by pressurized air that is sprayed onto the glass. Prior art roller hearth furnaces utilize roller conveyors for conveying the glass sheets through the furnace with their planes oriented horizontally and then to a quenching unit where the sudden cooling is performed. Prior art roller hearth furnaces are disclosed by the U.S. Pat. of McMaster et al, No. 3,806,312, issued Apr. 23, 1974, and by the references cited therein. Subsequent to the quenching, cooling units are used to further cool the glass to a temperature where it can be handled.